1. Field of the Invention
The present invention relates to display devices and, more particularly, to a method for displaying the current status of a display device adopting a display power management signaling (DPMS) standard, and an apparatus for achieving the same, which enables DPMS mode verification using an on-screen display (OSD) circuit.
2. Discussion of Related Art
A display device for use with a personal computer is generally manufactured with internal control means for reducing power consumption, such as the DPMS standard. In conformity with the DPMS standard, the host computer, which typically includes a video card, selectively supplies (or blocks) horizontal and vertical sync signals to the display device according to the computer's state of use, which is continually monitored in order to conserve power. Thus, a DPMS function enables the display device to manage its power distribution according to the presence (or absence) of the video sync signals. The power management states are classified into an "on" (normal) state, a standby state, a suspend state and a power-off state.
______________________________________ DPMS sync signal applied state horizontal vertical ______________________________________ on yes yes standby no yes suspend yes no off no no ______________________________________
As shown in the above table, both the horizontal and vertical sync signals are applied to the display device in the "on" state, only the vertical sync signal is applied in the standby state, only the horizontal sync signal is applied in the suspend state, and neither sync signal is applied in the power-off state. Starting in the "on" (normal) mode, the DPMS state converts, in sequence, first to the standby mode, then to the suspend mode, and finally to the power-off mode, according to a time lapse corresponding to the lack of use of the computer system. Power management in a computer is described in, for example: U.S. Pat. No. 5,586,333 to Chun-Geun Choi et al., entitled, Method And Control Apparatus For General Power Management Signal Of Computer Peripheral Equipment In A Computer System; U.S. Pat. No. 5,555,032 to Yung-Ken Kung entitled Integrated Circuit For Economizing Power Consumption Of A Monitor By Using Two Reference Values For Discriminating The Input Signal; U.S. Pat. No. 5,428,790 to Leroy D. Harper, et al., entitled, Computer Power Management System; U.S. Pat. No. 5,396,635 to Henry T. Fung, entitled, Power Conservation Apparatus Having Multiple Power Reduction Levels Dependent Upon The Activity Of the Computer System; and U.S. Pat. No. 5,389,952 to Dan Kikinis entitled Low-Power-Consumption Monitor Standby System.
In order to notify the user of the status of a display device adopting the above DPMS function, indicator lights (e.g., LEDs) may be installed on a display device, so as to have various colors and/or blinking patterns. This, however, would consume front panel space while increasing assembly costs and would necessitate that a user be well acquainted with specified states of the indicator or indicators through a guide (manual) provided by a display device manufacturer.
Meanwhile, if the signal cable (D-sub connector) for carrying video signals output by the main body of a personal computer to the display device becomes disconnected for any reason, the DPMS state should be set to the power-off mode to minimize power consumption However, in order to display a message for warning or informing a user of such a condition by driving an OSD circuit, the power necessary for normal operation must be applied to a display device, which defeats the purpose of the DPMS function.